Question: What is the greatest common factor of $10$ and $40$ ? Another way to say this is: $\operatorname{gcf}(10, 40) = {?}$
The greatest common factor is the largest number that is a factor of both $10$ and $40$ The factors of $10$ are $1$ $2$ $5$ , and $10$ The factors of $40$ are $1$ $2$ $4$ $5$ $8$ $10$ $20$ , and $40$ Thus, the greatest common factor of $10$ and $40$ is $10$. $\operatorname{gcf}(10, 40) = 10$